Caption:A lot of companies try to sell you their diet as the only one that works. The author of "Diet Cults" says it isn't so.

If you've ever rolled your eyes at a fad diet — or tried one and didn't get the promised results — you'll like what Matt Fitzgerald has to say.

A certified sports nutritionist and author of the bestselling "Racing Weight," Fitzgerald's new book is called "Diet Cults." Turns out there’s no one right way of dieting, as every trend claims, but rather sensible ways of being healthy that don't require a high tolerance for one kind of food (or totally avoiding another).

Most diet books are presenting a particular diet as the best diet or better than any other diet, but I’m not doing that. I’m first of all exposing the idea that there is a single best diet as false. Secondly, I’m making the argument that you can’t just eat anything you want and except to be healthy, but that human beings are very adaptable dietetically, so you can eat in a way that conforms to your culture and personal preferences and still be very healthy.

If you’re already following a diet – let’s say a vegan diet or a low-carb diet – and you're happy with it, I’m not trying to talk you out of eating that way. I’m trying to offer an alternative to people that are turned off by the restrictions of what I call the "diet cults."

Why are so many people and companies advertising there's-only-one-way diets?

I think the conventional answer to that question is money. There’s a competitive marketplace of diets. If you make a fabric softener, you’re going to say that it’s better than the other fabric softeners. It’s the same thing with diets.

But I also think there’s an ancient tradition to judging other people on how they eat that has nothing to do with capitalism. If you go back to ancient cultures, they tended to distinguish themselves from other cultures through their diets. We eat this way, those guys eat that way, and our way is better. I think there’s something deeply ingrained in us as humans that makes us identify deeply with how we eat and judge other negatively who choose to eat another way. That motivates us to evangelize on behalf of whatever diet we decided is the best.

What is the best advice for people who want to live a healthy lifestyle?

Keep it simple. The average fifth grader today knows enough about diet to eat in a healthy way that is also personally satisfying. The average fifth grader knows that you should eat lots of fruit and vegetables, and not a lot of soft drinks. You don’t really need to go too far beyond that.

What are people most confused about when they want to start a healthy diet?

When people make a decision to commit to a diet, usually they are past the confusion. They have accepted the doctrine that goes along with that diet. The people who are confused are the ones who are stuck between diets. They are exposed to all of them – each one presenting themselves as the only one that work – and that can a leave person confused. But the people that are submitted to the rules of this or that diet, usually they are not confused at all, they are very certain that they have chosen the right way.

What are the common mistakes people make when it comes to their diet choices?

The most common mistake is not keeping it simple and complicating things too much. An example would be deciding that carbohydrate is bad, all amounts of it are bad, and it’s bad in any context, and just going out of your way not eating carbohydrate even though some of the most familiar foods in most cultures are perfectly healthy foods with carbohydrates in them. That can really complicate your life, if suddenly things you grew up eating and enjoyed you don’t allow yourself to eat them anymore. And not with good reason. Whole grains are healthy, and they have a lot of carbohydrate. Bread and cereals also have a lot of that, but you can have a diet that includes those and is perfectly healthy. By focusing on a nutrient instead of the food, you can make things more difficult for yourself than they really need to be.

There are no shiny pictures of food in your book, just a few funny cartoons. Why?

One of the reasons why I included the cartoons was really to cue the reader that this is a different kind of diet book. I don’t read a lot of diet books because I find them insufferable. They tend to have a very sanctimonious and judgmental tone that I don’t like. A lot of the authors come off as jerks and I didn’t want to do that, so when I talk about people who are on different diets in the book I don’t try to make them look bad — I show that it can work for this person, but that doesn’t mean the underlying doctrine is true. I’m trying to change the tone of the debate. I’m a writer first, and a nutrient expert second, so I wanted to take readers on an unexpected adventure. I think the book you get is not the book you expect when you see the title and the cover, and that’s very intentional.

What do you hope people will get out of reading your book?

I’m hopeful that this concept of diet cults will catch on, so that in the future someone who’s read the book can smell a diet cult from a mile away. People try to focus on how the various diets are different, but I’m trying to show that on a deeper level they are actually all the same.